You're missing huge segments of income and deductions that are opaque to the IRS. In other cases, the information the IRS needs to calculate your tax isn't avai

You're missing huge segments of income and deductions that are opaque to the IRS. In other cases, the information the IRS needs to calculate your tax isn't available until everyone else files their taxes (cyclic dependency). Some examples: - Investors in a local restaurant may receive dividends which are not disclosed to the IRS until the restaurant files taxes. - Those dividends may reach a person via intermediaries. For example, a person receives her share of dividends from all the investments from an investment company in which she is an investor. That company may also have in turn invested into other investment companies. - A person inherits stock and migrates it to her brokerage account. Subsequently, she sells it. Neither the original brokerage nor her brokerage knows her cost basis and therefore can't know what portion of the proceeds are taxable. - Inheritances can get messy, in particular because in some cases the IRS needs to know the size of the estate where the inheritance originated in order to calculate the tax. - Taxes, tips, and direct crypto sales are all taxable events of which the IRS may have no data. - Rents: you don't tell the IRS how much rent you pay; the corollary is that the IRS doesn't know how much rent the landlord took in. And even if they did, to calculate the tax they also need to know the sum of expenses for the year. To calculate that, you may need to know the financing of the property. There are similarly many cases on the deductions side of the ledger where a naive approach will end up over-collecting from taxpayers (people would love that). (Yes, some of these could change if we changed our tax code. But that's not something the IRS is able to do.)